Anaerobic Oxidation of Methane: Progress with an Unknown Process

Abstract

Methane is the most abundant hydrocarbon in the atmosphere, and it is an important greenhouse gas, which has so far contributed an estimated 20% of postindustrial global warming. A great deal of biogeochemical research has focused on the causes and effects of the variation in global fluxes of methane throughout earth's history, but the underlying microbial processes and their key agents remain poorly understood. This is a disturbing knowledge gap because 85% of the annual global methane production and about 60% of its consumption are based on microbial processes. Only three key functional groups of microorganisms of limited diversity regulate the fluxes of methane on earth, namely the aerobic methanotrophic bacteria, the methanogenic archaea, and their close relatives, the anaerobic methanotrophic archaea (ANME). The ANME represent special lines of descent within the Euryarchaeota and appear to gain energy exclusively from the anaerobic oxidation of methane (AOM), with sulfate as the final electron acceptor according to the net reaction: CH(4) + SO(42-) ---> HCO(3-) + HS(-) + H(2)O. This review summarizes what is known and unknown about AOM on earth and its key catalysts, the ANME clades and their bacterial partners.

Stratified Communities of Methanogens in the Jiulong River Estuarine Sediments, Southern China

“…The most predominant phylotype affiliated with ANME-2a (38 % of total sequences) in libraries was represented by M151-3 (32 % of total sequences) and was closely related to AOM-Clone-E10 (97 %) from anaerobic methane-oxidizing sulfate-reducing enrichment [15]. Till date, it was well known that ANME2a was responsible for anaerobic methane oxidation in a variety of environments including clod seep, mud volcano, deep sea sediment, hydrothermal vent and coastal sediment [2]. Thus Methanosarcinales/ANME could be safely related to methane oxidizing archaea in our study.…”

“…Methane is an important greenhouse gas and has so far contributed an estimated 20 % of postindustrial global warming [2]. Marine sediments produce methane between 75 and 320 Tg year -1 which methanogens are mainly responsible for [3].…”

“…So estuaries contribute importantly to marine CH 4 emissions [10]. Methane production and consumption are spatially separated and conducted by different archaeal groups in the subsurface sediment environments [2]. Jiulong River Estuary located at south tropical region in Fujian Province, southern China.…”

Metabolic manipulation of methanogens for methane machinations

“…The first process used to capture methane anaerobically for biotechnology applications (Soo et al ., 2016) is based on the natural process of anaerobic methane oxidation (AOM), which efficiently captures up to 300 Tg of methane per year to limit global methane emissions (Knittel and Boetius, 2009). AOM occurs in natural consortia consisting of anaerobic methanotrophic archaeal populations and syntrophic bacteria.…”

“…Carbonate in the medium and methane in the headspace were converted into the two carbons of acetate as shown by 13 C labelling of both substrates (Soo et al ., 2016). These results in effect put an end to the decade's old debate about whether methane can be fixed by running methanogenesis in reverse (Knittel and Boetius, 2009). They also will now enable Mcr to be studied biochemically as it is produced for the first time in active form.…”